The present invention relates to a system for controlling the ground speed of a maneuverable off-road vehicle and, more specifically, relates to an interconnected system for controlling the ground speed of lawn and garden tractors and front mount mowers having hydrostatic transmissions.
It is known to provide off-road vehicles, specifically small tractors and front mount mowers with systems for controlling their ground speed. Such vehicles usually are equipped with conventional systems for: selectively operating the vehicle in either the forward or reverse direction (engine, transmission, drive train); selectively stopping the ground motion of the vehicles (brakes); and selectively utilizing the brakes to assist with vehicle's maneuverability (left and right turn brakes). It is also known to provide such vehicles with systems for: selectively maintaining a constant swash plate position without an operator engaging the accelerator or a "cruise control" and selectively disengaging the cruise control.
Additionally, it is known to be very desirable to initially precisely locate and establish the hydrostatic transmission's neutral position such that when in the neutral position, there is no ground movement or creep in either the forward or the reverse direction. Further, after initially establishing a precise neutral position, it is also desirable to either eliminate or at least reduce subsequent adjustments in order to maintain this initial precise location.
With respect to maintaining a constant swash plate position, it has long been desirable to develop not only a reliable cruise control system but one which incorporates a plurality of rapid disengagement means which, when necessary, allows an operator to rapidly disengage the cruise control system in order to regain normal control of the vehicle.
Another previously unrealized goal of designers in the art relates to means for preventing the vehicle from being driven with the parking brake partially engaged or for preventing the operator from accidentally depressing a forward or reverse control pedal such as when mounting the vehicle thereby causing the vehicle to accelerate in either the forward or reverse direction. The absence of means for preventing these conditions results in constant potential unsafe conditions. Additionally, without means for positively preventing the vehicle from being driven with the parking brake partially engaged, potential for causing excessive wear of the brake system is greatly enhanced.
Solutions to a number of these problems have been proposed. Specifically, it is well known to provide a throttle and a gear selector attached to the engine, transmission and drive train for selectively operating the vehicle in either the forward or reverse directions. It is also well known to provide a system for selectively stopping the vehicle when operating in the forward and reverse directions. It is further well known to provide foot brakes to assist with vehicle maneuverablity.
With respect to methods and apparatus for precisely locating the neutral position of a hydrostatic transmission, U.S. Pat. No. 3,488,955 commonly owned with the present application, illustrates one attempt to solve this problem. While the mechanical linkage disclosed did improve the initial location and subsequent return of the swash plate to the hydro neutral position, the tolerances between the cam roller and the groove, which increase, due to wear, with usage, did not satisfactorily reduce creep since due to these tolerances and subsequent wear, there was some movement of the swash plate. Since it is important that there be no movement of the swash plate when the transmission is in the neutral position and since creep can be caused by as little as one half of a degree or even less movement, the disclosed mechanical linkage proved somewhat inadequate over time.
Another problem with the linkage disclosed in the U.S. Pat. No. 3,488,955 involved the incorporation of a neutral start switch. Since there was quite a long linkage which ran from the operators location all the way back to the transmission, it was possible for the gear lever to indicate that the transmission was in the neutral position when the transmission swash plate was not in the netural position, thus, the netural start switch was not in the proper position and the vehicle would not start.
With regard to cruise control systems for off-road vehicles having hydrostatic transmissions, previously known systems have proven somewhat unreliable and have not incorporated at least three methods for positively effectuating cruise control disengagement.
A typical cruise control system utilizes a friction device to maintain the position of the swash plate. These friction devices present problems, since the tendancy of all hydrostatic transmissions under load, such as going up a hill, is to seek the neutral position, the friction contact is often prematurely broken resulting in the vehicle slowing down. This naturally requires that the operator place the vehicle back in the cruise mode by reengaging the friction device. Obviously any friction device will, over time, suffer from wear. Thus, the cruise controls containing friction devices require frequent replacement.
Accordingly, there is a need for an improved system and method for controlling the ground speed of a maneuverable off-road vehicle having a hydrostatic transmission which provides an operator with precise control of the vehicle. Such a system should have a precisely located neutral position; a foot controlled system for operating the vehicle in both the forward and reverse directions; a system for stopping the vehicle or brake system which includes: a left and right turn brake system for enhancing the vehicles maneuverability; a service brake system for emergency, rapid stopping and a park brake system; a system for selectively maintaining a constant swash plate position when the vehicle is being operated in the forward direction only or "cruise control" system; at least three positive, separate means for disengaging the cruise control and a system for interconnecting the cruise control system, the foot controlled operating system and the brake system.